I have a Craftsman 42" riding lawn tractor, a DYT 4000, that until now has run and worked perfectly. I recently replaced the deck drive belt with one of those green reinforced belts (#6997), and it ran fine until last weekend (I think the operator hit something). It now has a really bad vibration when the mower deck is engaged. The vibration seems to be in the deck itself, not from the engine or electric clutch. I replaced the blades and dissassembled the complete deck: checked for broken or damaged mandrel housings, examined the mandrel shafts for straighness (they appear unbent), checked the bearings (they appear fine), and cleaned the deck itself (removing grass and debris -- generally, just a really good cleaning). Everything checks out except both pulleys, which seem to have a bit of damage at the splined mounting holes; the splines are worn down a bit, but not completely (I know they're not true splines, more like teeth, but using the term "spline" helps me describe the problem). In addition, the matching splines on the mandrel shafts are worn. When the vibration started, the mower had thrown the new belt and the spring that tenses the idler pulley arm (the manual calls it "spring ext elect clutch") had come off. I'm not positive I have this spring correctly installed at the idler arm and belt tension seems a little light to me. What's happening and how do I fix it? Thanks for any help!

Are all the belts running smooth when you have the mower engaged, or are they "floppping" around? If they are not running smooth your tension could be incorrect. If the belts are all running smooth then your problem may be the worn spindle splines. In any case, I would look into getting the shafts/pulleys replaced. Those worn splines will probably only get worse. If you hit something, and that's when the vibration started, then something may be bent that isn't detected to the naked eye.

Yeah, that sounds feasible. I'll take a look at that belt. It sure didn't seem to be as tight as I thought it should be. So the vibration may be just the belt flopping around? I'll also check out the pulleys and spindles; that will just get worse as you say, so now is a good time to fix it. Geez, pulleys and spindles can't be THAT expensive, right? (ha!)

Check for a bent spindle, (I think the operator hit something) doesn`t take much, leave the blades on and rotate them. Also check for a broken ear on the spindle housing. Parts are not that expensive it`s the shipping charges that Sears adds on.

I checked the spindles just as you described. And checked the housings for broken ears -- I had this happen to me several years ago on another old mower, so it was one of the first things I looked for. Know what though? I just realized that I haven't checked the spindles with the new blades on -- those old blades may have given me false readings, don't you think?

I was given a Craftsman with a 42 inch deck this spring that had the same problem.http://www.mytractorforum.com/showth...303#post700303
PO had changed the spindle and not gotten the nut that holds the pulley on tight enough. The center of the pulley and the shaft had both been damaged. You will need to replace the pulley and shaft and tighten the nut to recomended tourqe

My Murray used to do the same thing right before one of the mandrels would give out. Upon inspection the mandrels would seem fine but within 30 minutes or so of use, the mandrel bearings would finally give out.......

New members with 0 posts, please do not ask me ?'s via p.m. Post on the open board so that all can benefit.

dan, my money is on the belt , take the belt off turn it inside out and look for worn , or thinner parts of the belt, that will make them jump and dance on the pulleys, just one thin spot, tom

Yea, like Declid said, don't count the belt out just yet. About two weeks ago my daughter was mowing, shut the deck off and drove to another part of the yard to continue mowing. When she engaged the deck she said, "there was this awful squealing and a lot of white smoke!". She had run over a good size stick with the deck off and it got lodged just right to not allow the blades to turn. When I got home, I removed the stick and man did that deck shake! So bad it wouldn't keep the belt on, and it was just a thin spot in the belt.

Yea, like Declid said, don't count the belt out just yet. About two weeks ago my daughter was mowing, shut the deck off and drove to another part of the yard to continue mowing. When she engaged the deck she said, "there was this awful squealing and a lot of white smoke!". She had run over a good size stick with the deck off and it got lodged just right to not allow the blades to turn. When I got home, I removed the stick and man did that deck shake! So bad it wouldn't keep the belt on, and it was just a thin spot in the belt.

Of course it will,,, if burned thin in spots, when that spot hits the pulley it will be a diff size, and u'll get a bump bump,, [vibration] we all come across this from time to time , if u work on mowers,,, tom

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